秸秆热解过程中有机氮转化机制及金属离子催化转化机理研究

Occurrence characteristics and chemical structure of nitrogen in straw are very different from those in coal, and the organic nitrogen transformation mechanism during straw pyrolysis process is great significance for clean biomass utilization. Firstly in this project, reverse micelles method will be used to extract crude protein of straw and then the pyrolysis experiment of crude protein will be carried out under the conditions of multi-factors coupling interactive effects. The distribution law of nitrogen-containing products will be grasped. Secondly, low-temperature pyrolysis of crude protein will be carried out at 300 ℃ to 500 ℃. The liquid nitrogen-containing compound will be analyzed and the nitrogen-containing model compound can be chose according to the results of the analysis. Density functional theory will be used to study the bond breaking reaction network combining with molecule structure model. The formation path and the reaction kinetic parameters of the target products can be confirmed by the experiment and modeling calculation. Furthermore, the inherent relationship mechanism between pyrolysis reaction conditions and target products will be acquired. Thirdly, the effect of different metal ions on the electronic properties and the chemical bond strength of model compounds will be calculated. The metal salts and model compounds co-pyrolysis experiment will also be carried out. According to the model calculation and experiment results, the pyrolysis mechanism of model compounds under the action of metal ions will be identified. Finally, the transformation mechanism of organic nitrogen will be clear in biomass pyrolysis process combining the experiment of straw crude protein and model compounds with theoretical calculations. And also the catalytic mechanism of metal ions on the nitrogen transformation will be obtained..The project combined with combustion, quantum chemistry and biochemistry cross-knowledge. The transformation mechanism of organic nitrogen during the pyrolysis of biomass and the catalytic mechanism of metal ions will be revealed in this project. The research will provide a scientific basis for the clean use of biomass.

秸秆中氮的赋存形态和化学结构与煤有很大差异，秸秆热解过程中有机氮的转化机理对其清洁利用意义重大。本项目首先采用反胶束法萃取秸秆粗蛋白，开展多因素耦合作用下粗蛋白热解实验，掌握含氮产物的分布规律；其次，根据粗蛋白低温热解实验液相含氮物质种类选择模型化合物，结合其分子结构模型采用密度泛函理论计算其化学键的断裂反应网络，继而开展模型化合物热解实验确定目标产物的形成路径和反应动力学参数，获得热解条件与产物之间的内在关联机制；再次，计算不同金属离子对模型化合物电子特性与化学键强度的作用，结合金属离子与模型化合物共热解实验，确定金属离子作用下模型化合物的热解机制；最后，结合粗蛋白与模型化合物热解实验和理论计算，获得秸秆有机氮的转化机制和金属离子催化转化机理。.本项目结合燃烧学、量子化学及生物化学等交叉知识，揭示秸秆热解过程中有机氮的转化机制及金属离子催化转化机理，为生物质的清洁利用提供科学依据。

针对典型农作物秸秆采用热重-红外联用及固定床实验系统，研究了秸秆种类、颗粒直径、升温速率、碱金属/碱土金属对其热解过程氮转化的影响，发现秸秆热解含氮气相产物主要为NH3、HCN、HNCO及NO，其中NH3产率最高HCN次之，其余含量较少。增加升温速率，气相含氮产物释放向高温区移动且产率增加，而焦炭氮产率降低，升温速率显著影响气相含氮产物生成的选择性。随燃料中H/N质量比增大，NH3的产量增加，HCN产量先增加后减少，HCN/NH3比下降。通过水洗和酸洗分别去除秸秆中内在碱金属及碱土金属，发现含氮气相产物释放向高温区域移动，反应活化能均有所增大，NH3、HNCO和NO的释放量呈增大的趋势，而HCN变化较小，焦炭N产率显著减少。脱除碱金属/碱土金属提高了NH3、HNCO和NO生成的选择性，而降低了HCN的选择性，HNCO的生成主要受碱土金属的影响。通过浸渍法添加外在碱金属/碱土金属，含氮产物在更低的温度区间便开始释放，热解活化能显著降低，且气相含氮产物产率明显下降，K能够抑制NH3、HNCO和NO的生成，而有助于HCN的生成，Ca能够抑制NH3、HNCO和NO的生成，但对HCN影响不大，Mg对四种氮化物均有抑制作用，三种元素对氮转化的影响能力为K＜Ca＜Mg。以甘氨酸酐和大豆蛋白为模型化合物研究了其热解过程氮释放的规律，随升温速率增加HCN和HNCO的产率增加，而NH3产率降低。K、Ca、Fe盐均对甘氨酸酐热解氮转化具有催化作用，其中K、Ca的存在有利于促进NH3、HCN的生成，Fe对HCN的生成具有促进作用，但对NH3的生成起到抑制作用。大豆蛋白热解时气相氮主要以NH3为主，约占总量的80%，HCN、NO和HNCO的释放量相对较少。添加碱金属及碱土金属盐类抑制了NH3生成的选择性，而增加HCN、NO、HNCO的释放。最后，基于密度泛函理论研究了典型模型化合物天冬氨酸热解反应过程，采用Materials Studio详细计算了天冬氨酸热解的关键反应路径，讨论了所有反应物、过渡态、中间体、产物的电子特性，研究表明Cα作为最活跃的位点进行热解反应，其中从Cα传递到Cβ的Hα的过程导致Cα-Cβ化学键的断裂，这个步骤是产生[HCN]过程的速控步，而Hα从Cα转移到N原子是导致NH3生成的关键路径，本研究可为秸秆洁净热解及气化技术开发提供基础支持。